1. Field of the Invention
The field of the invention relates to electrical power supplies generally, and more particularly to an electrical power supply for an X-ray tube and a method of implementing the same. An embodiment of the invention may reduce the intensity of an inrush current appearing when an electrical circuit powering the X-ray tube is turned on. Embodiments of the invention can nevertheless be applied to devices other than X-ray generators.
2. Description of the Prior Art
There are known ways of limiting the appearance of an inrush current by the positioning, between the source and the generator, of a switch as well as a resistor, known as a limiting resistor. This series-connected resistor with a value R restricts the value of the current intensity to the value E/R, E being the value of the rectified current.
The resistor should nevertheless provide for the power throughput needed for the x-ray exposures. It is therefore necessary to find a preliminary compromise value for this resistor.
Furthermore, the resistor remains present throughout the working of the power supply. It therefore induces permanent electrical power consumption.
Another prior art device places a first switch, called a secondary switch, in a series connection with the limiting resistor and in a bypass in order to power the generator directly.
The bypass includes a main switch parallel-connected with the assembly formed by the resistor and the secondary switch. In this case, the secondary switch is closed when the system is started up in order to charge the capacitor of the high-voltage generator.
Then, in a second stage, the main switch is closed while at the same time the secondary switch is opened in order to remove the limiting resistor.
However, in practice, this type of assembly calls for a minimum of operation and safety on the part of the logic circuit in order to control the two switches. For example, this minimum implies that the main contractor should be closed only after the complete charging of the capacitor, that the contractors should not be closed when they are crossed by current, that security should be provided in the event of non-functioning of the main contact.
The logic circuit must also take account of the fact that the power is called up exposure by exposure.
Active switches with a precharging and charge transfer circuit are then used; for example contractors. However, these components are unreliable, relatively complex to implement, and costly.
In the case of a battery power supply, there also exist systems of connection with time-lagged contacts, the first contact setting up the precharging circuit, the second contact then setting up the direct path. This rustic solution has the drawback of producing an arc when the first contact is set up and, above all, of allowing the generator to be permanently powered by the battery (entailing problems of battery discharge, reliability, safety).
What is needed is an apparatus and method configured to limit the appearance and effect of this inrush current to the maximum extent